The invention concerns a composition for the production of shaped bodies and a method for the production of shaped bodies made of such a composition.
The increased supply of mineral oils and their thermal processing for producing energy as well as their synthesis into plastic material has led to a steady increase in the carbon dioxide content (CO2) of the earth""s atmosphere. The rising CO2 content in the atmosphere is made partly responsible for the global greenhouse effect and the resulting climate changes of the earth. To limit accumulation of CO2 in the atmosphere, it is necessary to close the CO2 cycle. This means that only an amount of CO2 should be given off into the atmosphere within a certain time period which nature can transfer into organic solid matter through photosynthesis. This is, however, clearly not the case for plastic materials gained synthetically from crude oil. Synthetic plastic materials cannot be disposed of in a CO2 neutral fashion after their period of use since more plastic waste is burned than crude oil produced by renewed synthesis, which unavoidably results in CO2accumulation in the atmosphere.
The major group of synthetic plastic materials is thermoplastic materials. They are transferred into a plastic state using extruders, injection molding machines or hot-shaping presses under the influence of energy either as heat or friction, and are formed, in molds or tools, into the desired shaped body. If it were possible to generate a material which is exclusively gained from rapidly growing resources and which could be easily processed with conventional thermal shaping machines, the balance would be considerably better with regard to both ecology and economy.
There are a few natural materials which would be suitable for such applications e.g. in particular polysaccharides (cellulose, starch) proteins or lignins. However, thermal shaping of these polymers is problematic and materials which must be reinforced with fibers to stabilize their shapes, e.g. cellulose fibers, require the addition of a natural processing aid. Shellac has proven to be such a processing aid in accordance with the invention. Shellac is produced by the louse xe2x80x9ckerria laccaxe2x80x9d to protect their eggs from external weather effects and can be melted at temperatures of around approximately 80xc2x0 C. The good film forming properties of shellac contribute to favorable processing properties of the natural fiber mixture using extruders, injection molding machines or presses.
In accordance with the invention, lignin is used as a further thermoplastic binding agent for natural fibers which is derived from the most different cellulose disintegrating methods. However, the thermoplastic behavior of lignin after cellulose disintegration is poor and is insufficient for shaping it into a thermoplastic compound with natural fibers.
Only a combination of the natural fibers, e.g. cellulose (as reinforcing material or filler), lignin (as binding agent for the fiber) and shellac (as processing aid) leads to compounds which can be processed and having good mechanical and thermal properties which are solely made from growing raw materials and are suitable for high quality technological applications.
In contrast to known attempts with compositions of mostly natural components (EP 0 720 634), the inventive composition in accordance with the claims offers the following advantages:
compounds of 100% growing raw materials (closed CO2 cycle),
direct processing of flowable mixtures (no thermal pre-stages for the generation of the mixture which protects the mixing components and reduces odor due to the reduced portion of disintegrated products),
cold compacting with poorly flowable mixtures (no thermal loading which protects the mixing components and reduces odors through reduced portion of disintegrated products),
no proteins (less expensive compounds, reduced danger of mold in the compounds or the shaped parts),
no acid is used (reduced wear of the processing machine or the tools),
no glycol or glycerin (no unhealthy emissions during processing),
all lignins from all cellulose disintegration methods can be used (ligneous sulfonates, kraft lignin, lignin in organic solution, lignin in water solution)
low processing temperatures are possible through shellac (no thermal loading to protect the mixing components and reduce odor due to reduced portion of disintegrated products).
In a preferred embodiment of the composition in accordance with the invention, the composition contains up to 80% lignin, up to 80% natural fibers, and up to 70% shellac. The natural fibers of the composition in accordance with the invention preferably have dimensions between 10 xcexcm and 10,000 xcexcm. With regard to the method in accordance with the invention, a preferred embodiment thereof comprises the additional step of adding native oil sliding agent to the dry mixture. The sliding agent is preferably added prior to the first step of the method in accordance with the invention in which the dry mixture of polymer lignin, shellac, and natural fibers is thermally plastify. Alternatively, the sliding agent can be added during this step.
The flowable powdery mixtures in accordance with the invention or the cold-pressed granulated matter of cellulose fibers or powder with lignin and shellac can be used wherever plastic materials or naturally grown wood is used in shaped parts or work pieces, e.g. in the automotive, construction, furniture, packing, or electronic industry.